Method for forming a sacrificial anode

ABSTRACT

The present invention is directed to an improved method for protecting ferrous pipe from corrosion and comprises affixing in intimate contact with said pipe a length of magnesium tubing. The magnesium tubing, having sacrificial anode properties, is slipped over a length of ferrous pipe while at an elevated temperature. The tubing is then compressed by external pressure until it is in intimate contact with the ferrous pipe throughout its length and it is allowed to cool in place.

United States Patent Scherer et al.

[ 1 .iune 119, R973 METHOD FOR FORMING A SACRIFICIAL ANODE Inventors: John G. Scherer; Lewis W. Taggart,

both of Tulsa, Okla.

Assignee: Kaiser Aluminum & Chemical Corporation, Oakland, Calif.

Filed: Apr. 30, 1971 Appl. No: 138,969

us. 01 29/447, 29/516, 204/197 B23p 11/02 Field of Search 29/516, 447;

References Cited UNITED STATES PATENTS 2/1956 Brooks et a1 204/197 X 2,768,433 10/1956 ODonnell.... 29/447 3,251,427 5/1966 Ewing 204/197 X 3,558,463 1/1971 Strobach et zal 1. 204/197 Primary Examiner-Charlie T. Moon Attorney-Paul E. Calrow and Harold L. Jenkins [57] ABSTRACT The present invention is directed to an improved method for protecting ferrous pipe from corrosion and comprises affixing in intimate contact with said pipe 21 length of magnesium tubing. The magnesium tubing, having sacrificial anode properties, is slipped over a length of ferrous pipe while at an elevated temperature. The tubing is then compressed by external pressure until it is in intimate contact with the ferrous pipe throughout its length and it is allowed to cool in place.

1 Claim, 1 Drawing Figure mzmww 3.739.456

. INVENTORS dorm G.SCHERER LEWIS W. TAGGART J' H ATTORNEY METHOD FOR FORMING A SACRIFICIAL ANODE BACKGROUND OF THE INVENTION Sacrificial anodes have been used to protect ferrous metal for a considerable period of time. They have been used in a variety of circumstances, including the protection of piping that is buried in the ground. In general, the prior art has provided a separate anode which must be electrically connected in the field to a length of pipe to be protected. This was generally accomplished through lead wires from the pipe to the anode. The pipe and anode were then buried in the ground. This method has had certain disadvantages associated therewith. For example, not infrequently, the field worker would forget to attach the anode to the. pipe prior to burying in the ground or would improperly connect it to the pipe so that it failed to function as intended. Even when the anode was properly attached, they would sometimes become electrically disconnected from the pipe by having one or more of the leads severed by a plow, spade, or other groundworking equipment.

BRIEF DESCRIPTION OF DRAWING The FIGURE is a fragmented perspective view of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The difficulties encountered with the prior art structures are overcome by having the magnesium anode permanently affixed at the manufacturing facility to the pipe to be protected. This is accomplished by taking a tube of magnesium which has sacrificial properties, heating it to an elevated temperature at which it will flow when subjected to external pressure, slipping the tube over a length of ferrous pipe, compressing it until the metal of the tube is in intimate contact throughout the length of the tube with the ferrous pipe and allowing it to shrink fit in place by cooling. As a practical matter, the inner diameter of the magnesium tube should be as close to the outer diameter of the ferrous pipe as possible and still allow it to slip over the pipe with ease. The relative sizes of these diameters will depend upon the dimensional tolerances of each. While it is theoretically possible to place a magnesium tube having an internal diameter at the elevated temperature employed that is only 0.002 inch greater than the external diameter of the ferrous pipe, the commercial products simply are not manufactured with this degree of accuracy. Therefore, the diameter of the tubing must be selected with these variations in mind.

The weight of the magnesium anode in relation to the amount of pipe to be protected will vary depending upon circumstances. Primarily, this will be influenced by the nature of the soil into which the ferrous pipe is placed. It will also depend to some extent upon the pe riod of time during which the pipe is to'be protected. In one application and as illustrated in FIG. I, a magnesium tube weighing 1% pounds has been used successfully. In this instance, a tube 1 having an overall length of approximately 8 inches and a wall thickness from about A inch to about Va inch is placed over a 7 to 10 foot length of ferrous pipe 2 which has an external diameter of approximately 1 inch. The tube, which had been formed by extrusion, had an internal diameter of about 1.1 inches and was at a temperature of about 400F. It was forged onto the pipe at a pressure of about 4,000 psi and allowed to shrink fit by cooling. This pipe then is used to connect a meter with a length of pipe which may be metal or plastic, and through these, gas is conducted from a main line to the meter. In this instance, the portion of the pipe to which the magnesium is attached is buried under the ground.

The temperature of the magnesium anode or tube when placed over the ferrous pipe should be high enough so that it will flow with reasonable facility when subjected to reasonable external pressures. For example, temperatures from 300F. to 800F.'have proven useful; in any event, it should be below the ignition temperature of the anode. The ignition temperature is a function of the particular alloy employed. In addition, the temperature of the magnesium anode should be high enough to allow it to form a shrink fit with the ferrous pipe when it is cooled. The external pressures, as indicated above, can vary considerably, e.g., from 2,500 psi to 6,000 psi, preferably from 3,000 psi to 5,000 psi. Between the use of pressure and the shrink fit, an excellent seal with the ferrous pipe is obtained, making it most unlikely that the anode will accidentally disengage from the pipe at a later time.

The magnesium metal of the tube or anode may be any alloy having the required sacrificial properties and the anode may be extruded or cast. The extruded form is preferred when the alloy lends itself to this method. Specific alloys that may be employed are AZ3l, which contains approximately 3 percent aluminum, 1 percent zinc and 0.5 percent manganese. This alloy may be used to form the magnesium tubes by extrusion. Another alloy which may be employed is basically pure magnesium with 0.5-1.5 percent manganese. A third useful alloy will contain basically 6 percent aluminum, 3 percent zinc and the balance magnesium. This alloy would be formed into the required tube shapes by casting.

We claim:

1. A method for forming a sacrificial magnesium anode integral with a length of ferrous pipe to be pro tected comprising heating a magnesium alloy tube having sacrificial properties and a wall thickness from about one-eighth inch to about three-fourths inch to a temperature from about 300 to about 800F, slipping said heated tube over the length of ferrous pipe having an external diameter less than the inner diameter of said tube, subjecting the heated magnesium alloy tube to forging under a pressure of from about 2,500 psi to about 6,000 psi to cause the metal of the tube to flow into contact with the outer surface: of the ferrous pipe throughout the length of the tube and then shrink fitting said magnesium alloy by cooling thereby ensuring an intimate interfacial joint contact between the magnesium alloy tube and the outer surface of said ferrous pipe throughout the length of said tube. 

